Coding extensions

A Sonar plugin is a set of POJOs (Java objects) which implement extension points. These extension points are interfaces or abstract classes which model an aspect of the system and define contracts of what needs to be implemented. They can be for example pages in the web application or sensors generating some data.

The extensions implemented in the plugin must be declared in the plugin entry point, which is a Java class extending org.sonar.api.Plugin. This class must then be declared with the property <pluginClass> of the Maven plugin 'sonar-dev-mojo' :

Extension points

Here is list of extension points available in the sonar plugin API. Please note that partial implementation of those extensions are available in the api as well. Check the Javadoc for more information.

What

Since

Description

org.sonar.api.charts.Chart

1.10

Image generated by JFreeChart.

org.sonar.api.web.CodeColorizerFormat

1.12

Extend the library sonar-colorizer to support new languages. By default only Java sources are colorized in Sonar.

org.sonar.api.batch.CpdMapping

1.10

CPD definition to detect duplicated lines on a new language

org.sonar.api.batch.Decorator

1.10

Used to decorate resources, i.e. calculate measures from other measures. Example : the number of lines of code of a package is the sum of the lines of its classes.

org.sonar.api.web.Footer

1.10

Static HTML footer displayed in all pages.

org.sonar.api.resources.Language

1.10

Define a new language.

org.sonar.api.batch.maven.MavenPluginHandler

1.10

Define a Maven2 plugin to execute before analyzing the project.

org.sonar.api.measures.Metrics

1.10

List new Metrics. A metric is an instance of org.sonar.api.measure.Metric. It can be quantitative (lines of code, number of rule violations) or qualitative (code coverage, complexity by class, rules compliance). As a rule, a metric is used to store a number but it can also be used to store a text field with list of key/value pairs, an XML or even binary data.

org.sonar.api.web.GwtPage

1.11

Add a page, linked from the left sidebar. The page is implemented as a GWT component. GWT RPC/servlets are not supported.

Enables to ignore violations. Has a very simple interface : public boolean isIgnored(Violation violation). A NoSonarFilter draft has been added to the Squid plugin.

Sensor or Decorator ?

There are two extensions that enables to save measures : Sensor and Decorator. A common problem when writing a plugin is to decide which one to use.

Sensor

A Sensor is invoked once during the analysis of a project. The sensor can invoke a maven plugin, parse a flat file, connect to a web server... For example the Cobertura Sensor invokes the Codehaus Cobertura MOJO. Then the generated XML file is parsed and used to save the first-level of measures on resources (project, package or class).
A sensor has can access and save measures on the whole tree of resources. Sensor are generally used to add measure at the lowest level of the resource tree.

Decorator

Decorators are triggered once all sensors have completed. Their decorate method is called on every resource of a certain level bottom up. Decorators can load (SELECT) and save (INSERT) measures. The call is contextual, i.e it is only possible to access the resource and its children.
Decorators are generally used either to consolidate at higher levels measures that have been added by Sensors at the lowest level.